Is there any way to execute commands through VMware Tools for those VMs that I do not have a valid login for?
Interestingly, I'm gathering this info for our security team!
Not afaik, you will have to provide GuestCredential on the Invoke-VMScript cmdlet.
Or call the Invoke-VMScript with an account that also has rights inside the guest OS.
If you don't, this for example
Get-VM MyVM | Invoke-VMScript -ScriptType Bash -ScriptText "uname -a"
will fail with this type of error